1. Technical Field
The present disclosure relates to a sewing machine provided with a needle bar rocking mechanism which rocks a needle bar.
2. Description of the Related Art
Household sewing machines are generally provided with a needle bar rocking mechanism which is driven by a stepping motor serving as a drive source to rock a needle bar right and left, so that zigzag stitches can be formed on a workpiece cloth while the needle bar is rocked right and left. In this case, a needle plate is formed with a needle hole which is elongate in the right-left direction according to the rocking of the needle bar. Other than the zigzag stitches, the needle bar (a needle) is moved by a predetermined amount leftward from a middle baseline serving as a reference position to a left baseline or rightward from the middle baseline to a right baseline, so that a sewing operation is then carried out.
The aforesaid right and left baselines are determined so that predetermined clearances are defined between a needle location of a needle and right and left edges of the needle holes respectively. More specifically, the right and left baselines are set at respective predetermined positions so that the needle is prevented from interfering with the needle plate. However, when a sewing machine body is subjected to a large impact such as by falling or a screw has been loosened in a mechanism, there is a possibility that the needle location may be displaced from a normal location. Such displacement of the needle location may result in an undesirable sewing operation. In a serous case, the needle would interfere with the needle plate with the result of breakage of the needle or the like.
In view of the above-described problem, a reference mark is conventionally affixed on a part of the needle hole of the needle plate. The operator visually confirms whether the needle location corresponds with the reference mark. However, the operator cannot visually determine the displacement of the needle location accurately (objectively). As a result, affixing the reference mark is less reliable. In view of the circumstances, an improved sewing machine has been proposed which is provided with a proximity sensor mounted on a connecting rod transmitting a drive force of the stepping motor of the needle bar rocking mechanism to the needle bar, for example. A rocking position of the needle bar is detected by the proximity sensor so that an amount of rock of the needle bar is adjusted based on the detected rocking position.
In the above-described construction, however, the rocking position of the needle relative to the needle hole is detected in an indirect manner based on the detection of a detected part of the connecting rod by the proximity sensor. This indirect detecting manner results in a difficulty in an accurate detection of the rocking position of the needle relative to the needle hole.